Expanding Your Vocabulary - Head First HTML and CSS - page 345

Specify color using hex codes

Now let's tackle those funky-looking hex codes. Here's the secret to them: each set of two
digits of a hex code just represents the red, green, and blue component of the color. So the
first two digits represent the red, the next two the green, and the last two represent the blue.
Like this:

Alw ays start a hex code
wit h the # sign.

#cc6600

green

Wait a sec, how is “f”
or “c” a digit? Those
are letters!

Believe it or not, they are digits, but they're
written using a notation only a computer
scientist could love.

Here's the second secret to reading hex codes: each set of two
digits represents a number from 0 to 255. (Sound familiar?)
The problem is that if we used numbers, we'd only be able to
represent up to 99 in two digits, right? Well, not wanting to be
constrained by something as simple as the digits 0-9, computer
scientists decided they could represent all 256 values with the
help of some letters too (A-F). This is the hexadecimal system of
numbering, or “hex” for short.

Let's take a quick look at how hex codes really work, and then
we'll show you how to get them from color charts or your photo
editing application.